Peripheral Devices

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• What are the input/output devices connected to the computer?
• How the bus is connecting different modules in a computer?

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Memory and I/O Organization Memory Hierarchy, Associative Memory, Cache Memory, Virtual memory.

I/O Organization: Peripheral devices, I/O interface, Asynchronous data transfer, Modes of transfer, Priority interrupt, direct memory access and IOP

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Unit-4

What you’ll learn

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• Any component, inside or external, that adds new hardware capabilities to the basic design of a computer.
• For example: hard drives, printers, mouse etc.

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Peripheral

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• Facsimile (FAX): Application that converts and sends the white and black areas of a page over telephone wires or wireless networks to a receiving machine that converts the coding back into white and black areas and prints the message.
• Basically a fax machine is a remote copying device that transmits/receives copy to/from a remote location.

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Fax (Facsimile)

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Joystick

An Input device that positions cursor on a screen

• Used primarily for dynamic graphics at workstations and for video games.

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• A keyboard (which commonly resembles a type writer’s keyboard) provides input capability in most terminals.
• Keyboard equipped terminal converts the character(s) indicated by the pressed key into a serial bit stream for transmission over a data link.
• Each character is represented by a code, generally either ASCII or EBCDIC

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Keyboard

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• Text keys: A to Z, the numbers 0-9 and special characters.
• Control keys: Communication control codes, such as START, STOP, DELETE, and END OF TRANSMISSION.
• Function keys: which include carriage return, backspace and horizontal tab. Some terminals:
• Use auxiliary function keys to enable the user to program special operations (WWW key which connects directly to internet).
• Have only function keys, each key represents an item, key pressing actually enters its identification and additional information.

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Keyboard Keys

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Virtual/soft/touch screen keyboard: On handheld computers, the keyboard is displayed right on the computer screen.

• Text can be entered by tapping the keys with finger or a pen like stylus.

Ergonomic keyboard:

• Repeated use of keyboards over long periods will result in physical stress on wrists and arms.
• By incorporating ergonomic designs, keyboards can be designed to have less physical stress.

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Other Keyboards

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Stylus: It is a pen style device that allows the user either to touch parts of a predetermined menu of options or to hand write information into the computer.

• The technology may respond to pressure of the stylus, or the stylus can be a type of light pen that emits light that is sensed by the computer.

Light pen: It is a pen shaped I/O device. It can be used to write or sketch or erase certain lines on the video monitor of the computer. It is also used for inputting graphics and reading bar codes.

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Stylus and Light Pen

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Track stick: Pencil eraser type pointing device located in the center of the keyboard, often found in notebook computers.

Numeric pad: Which will have only number keys.

• It facilitates rapid entry of numeric data to the terminal or the application may be dialing a number as in telephone handset

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Track Stick and Numeric Pad

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Converts a digital data stream into an analog form for transmission across an analog telephone network.

• Modulation: Prior to transmission of the data.
• Demodulation: Reconvertion of the received signal back into its form.

Each access port to the network requires a full duplex (two way simultaneous) capability, the device must perform both the modulation and demodulation functions; hence the name MODEM.

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Modem (Modulator and Demodulator)

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Hand held device used to point a cursor at a desired place on a computer screen;

• a click instructs the computer to take some action.

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Mouse

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Mouse without having a wire connection to the computer.

• It senses hand motion and transmits a signal to the computer to move the mouse pointer in the same direction.
• Buttons on the cordless mouse allow clicking, double clicking and dragging.

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Cordless Mouse

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• It has a beam of light that shines onto a special mouse pad that has lines on it.
• By moving the mouse across these lines, the crossing is picked up by the light from the mouse hitting the pad and reflecting back to a sensor in this mouse.
• Since there are no moving parts, the rate of failure is low and has higher reliability than mechanical mouse.

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Digital Mouse/ Optical Mouse

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Touchpad: It is a flat rectangular pad that senses the movement and pressure of fingertip to control the mouse point.

• Using finger gestures, one can click, double click, and drag just as with a mouse

Trackball: It is an upside down mouse, which is common in laptop computers.

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Trackball and Touchpad

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A touch pad used to create drawings using the same kind of hand motion used for sketching and tracing drawings.

• It uses a pencil like stylus instead of finger as in touchpad.

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Graphics Tablet

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With digital cameras and camcorders direct digital entry is available for graphics and full motion video.

• Light enters the camera through the lens.
• The light is focused on the charge coupled device (CCD), a solid state chip made up of tiny, light sensitive photosites.
• When light hits the CCD, the photosites convert light into electrons, which are then converted into digital information and is stored in the camera’s memory.

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Digital Camera

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Using microphone converts speech into digital form. It compares the patterns produced by the speaker’s voice with a set of pre-recorded patterns.

• Radiologists can dictate their interpretations of X-rays directly into transcription machines.
• Nurses can fill out patient charts by talking to computer.
• Warehouse workers are able to speed inventory taking by recording inventory counts verbally.

e.g., Viavoice form IBM

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Voice Recognition System

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Biometric devices identify a person through a fingerprint, voice intonation, or other biological characteristic.

• Fingerprint readers in keyboards and smartphones, so fingerprints could replace passwords.
• Retinal identification devices use a ray of light to identify the distinctive network of blood vessels at the back of one’s eyeball.

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Biometric

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There are varieties of scanners depending on the utility, resolution and colour depth (the number of colours that a scanner can sense and recreate)

• Flatbed scanner
• Sheet fed scanner
• Drum scanner
• Hand held scanner
• Card scanner
• 3D scanners (medical CAT scanners)
• Barcode scanner

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Scanners

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Variety of barcode scanners:

• A wand is an inexpensive scanner that requires physical contact as it is scanned across a bar code.
• Charge coupled device (CCD) scanners have a reading head. It is placed over a bar code and the trigger is pulled.
• Fixed focus optics (FFO) scanners are aimed at a bar code up to 20 inches away.
• Laser scanners use a laser beam to read a barcode.

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Barcode Reader/Scanner

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In Universal Product Code one can cross check the correct operation of scanner by tallying with “check digit” printed at the extreme right bottom corner on the label.

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There is a variety of bar code scanners are in use:

• A wand is an inexpensive scanner that requires physical contact as it is scanned across a bar code.
• Charge coupled devices (CCD) scanners have a reading head. It is placed over a bar code and the trigger is pulled.
• Fixed focus optics (FFO) scanners are aimed at a bar code up to 20 inches away.
• Laser scanners use a laser beam to read a barcode, when the trigger is pulled.

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Barcode Scanners

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MICR (Magnetic Ink Character Recognition): Recognition of characters printed with a special magnetic ink.

e.g., Characters printed at the bottom of the bank checks.

OMR (Optical Mark Recognition): Reads pencil marks and converts them into computer usable form.

e.g., Reading of answers from GRE paper.

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MICR and OMR

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It is accomplished using scanner and OCR software as follows:

• Scanned document is converted to a bitmapped image.
• The OCR software analyses the light and dark areas on the page, making a guess at how the page is laid out.
• The software looks up each character in its library of character templates trying to find a match for it.
• Unidentifiable characters are displayed as special symbols.
• After the conversion, the document can be saved in the format of word processing program and it can be edited.

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OCR (Optical Character Recognition)

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A monitor is an output device capable of displaying text and graphics.

Flat panel display: A very narrow display that uses one of several technologies, such as electroluminescence, LCD, or thin film transistors.

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Display Monitors

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CRT Monitors

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• The Cathode Ray Tube consists of a glass vacuum tube that contains one electron gun for a monochrome display, or three (red, green, and blue) electron guns for a colour display.
• Electron beams from these guns sweep rapidly across the inside of the screen from the upper left to the bottom right of the screen.
• Low price and easy implementation of colour displays.
• Bulky size and high power consumption.

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CRT Monitor

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• It uses electric current to align crystals in a special liquid.
• The rod shaped crystals are contained between two parallel transparent electrodes, and when current is applied, they change their orientation, creating a darker area.
• Applications: Watches, calculators, notebook computers and many other devices where small sized displays are needed.

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LCD (Liquid Crystal Display)

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• Plasma panels consist of two glass plates separated by a thin gap filled with a mixture of argon and neon gas.
• Advantage: High resolution, very bright, high contrast and very large panels can be built.
• Disadvantage: Very expensive.
• Applications: Found in applications where display quality is important and the bulky size of a cathode ray tube is undesirable.

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Plasma Display

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A special monitor that lets the user make choices by touching icons or graphical buttons on the screen. Touch screen systems are used for interactive displays in museums and in automatic teller machines.

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Touch Screen

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Output device that transforms digital computer content into a printed, paper based form.

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Impact printer: Output device that uses striking action to make impressions on paper.

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Character printer: These printers print on character at a time.

e.g., Daisy wheel printer.

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Printers

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Dot matrix printer: In these printers, a collection of dots forms each of the printed characters.

Advantages:

• Inexpensive.
• Produces draft quality and near letter quality.
• Can output some graphics.
• Can print multipart forms.

Disadvantages:

• Noisy.
• Cannot produce high quality output of text and graphics
• Limited fonts.

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Dot Matrix Printer

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Non-impact printer: Uses laser beams or streams of ink, rather than striking action, to make images on paper.

Thermal printers/ Dye sublimation printers: They use coloured waxes and heat to produce images by burning dots on special paper.

Advantages:

• Quite
• High quality colour output of text and graphics
• Can also produce transparencies.

Disadvantages:

• Special paper required
• Expensive
• Slow
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Non-impact Printer

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Inkjet/Bubble jet printer: It is a non-impact printer that shoots fine streams of ink onto paper. Each drop is produced by contracting the nozzles which out the liquid.

• These are less expensive than laser printers, but offer somewhat less resolution quality.
• Liquid inkjet: uses liquid ink.
• Solid inkjet: uses solid ink sticks

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Inkjet/Bubble Jet Printer

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• Removable ink cartridges are attached to printheads with firing chambers and nozzles apiece.
• As the print heads move back and forth across the page, software instructs them, where to apply dots of ink, what colours to use, and in what quantity.
• A matrix of dots forms characters and pictures. Colours are created by layering multiple colour dots in varying densities

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How Inkjet Printer works?

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• It is a non impact printer that uses laser beams to write information on photo sensitive drums, over which paper and toner pass, making images on paper.
• Laser printers are high speed, high quality devices which produce very high-resolution text and graphics, making them suitable for desktop publishing.

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Laser Printer

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• A laser beam is turned on and off by the stream of 1s and 0s.
• A rotating mirror deflects the blinking beam and paints a line across an electrically charged revolving drum.
• If the beam is on when it passes a point on the drum, it charges the dot that can attract toner. The toner is transferred from the drum to the paper under heat and pressure.

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How Laser Printer works?

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Line printer: Prints a complete line at a time, rather than printing one character at a time (dot matrix or daisy wheel printer), or one page at a time (laser printer).

• Line printers are very high speed printers, and are common in the corporate environment where they are used with mainframe computers.

Label printer: A printer specifically designed to print names and addresses onto continuous labels.

Photo printer: A printer designed to print photographic quality snapshots from digital cameras etc.

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Line Printer

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Uses computer directed pens to create high quality images.

• Flatbed plotter: Moves a pen up and down across a flat drawing surface.
• Drum plotter: Paper is fixed on a drum and pen moves only from side to side.
• Multicolour plotters use multiple pens to produce colours.

e.g., Pen plotters, electrostatic plotters, dot matrix impact plotters.

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Plotters

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Digital press: It is designed to print a large number of copies of magazines or books. They eliminate the need to make ready copies as in offset printing.

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3D printer: Squeez out molten plastic through a tiny nozzle that it moves around precisely under computer control. It prints one layer, waits for it to dry, and then prints the next layer on top

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Digital Press

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Sound output devices produce digitized sounds, ranging from beeps and chirps to music.

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Voice synthesizers or voice output devices convert digital data into speech like sounds.

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Voice Synthesizers

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VR Player: A media player designed specifically to watch immersive content with an head mounted display.

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AR glasses: Augment the perceived reality of users with information via light displays in the users' view.

• The system is hands-free and support even when the user is actively performing tasks with their hands

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Virtual and Augmented Reality

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Buses

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A shared communications path consisting of one or a collection of lines and the circuitry and chips that manage the transfer of data from one device to another on these lines.

Examples:

• Omnibus (PDP-8),
• Unibus (PDP-11),
• Multibus (8086),
• IBM PC bus (PC/XT),
• ISA bus (PC/AT),
• EISA bus (80386),
• Microchannel (PS/2),

• PCI bus (many PCs),
• SCSI bus (many PCs and workstations),
• Nubus (Macintosh),
• Universal serial bus (modern PCs),
• Firewire (Consumer electronics),
• VME bus (Physics lab equipment) and
• Camac bus (high energy physics).

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Bus

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• Advantages of the bus organization are versatility and low cost.
• By defining a single connection scheme, new devices can easily be added, and peripherals can even be moved between computer systems that use the same kind of bus.
• Buses are cost effective because a single set of wires is shared in multiple ways.
• The major disadvantage of bus is that it creates a communication bottleneck, limiting the maximum I/O throughput.

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Bus Organisation

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In some computer systems, a common bus connects CPU, memory and I/O components.

• Since the lines are shared by all components, only one component at a time can successfully transmit.

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A PC’s motherboard has a bus, such as ISA or PCI, but there are also buses between memory and the processor and external components, such as a SCSI or Universal serial bus.

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Bus Organisation contd..

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• Single bus structure
• Compatible input/output bus structure
• Multiple bus structure

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Bus Structures

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Bus performance is evaluated with the following parameters:

• Programmed I/O data rate
• Interrupt processed I/O data rate
• Direct Memory Access speed
• Memory bus data rate
• I/O bus data rate
• System overloading (task cannot be performed because the bus is busy)
• System overhead (activity required, but that is not part of the data transmission)

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Bus Performance

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Synchronous bus: A bus that includes a clock in the control lines and a fixed protocol for communicating that is relative to the clock.

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Asynchronous bus: A bus that uses a handshaking protocol for coordinating usage rather than a clock; can accommodate a wide variety of devices of differing speeds.

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Backplane bus: A bus that is designed to allow processors, memory and I/O devices to coexist on a single bus. It is a printed circuit on which many connectors are used to plug in functional boards.

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Buses

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System bus: A bus used to interconnect major computer components (CPU, memory, I/O) consisting of shared signal paths and utility lines, is built on the backplane bus. This system bus provides a common communication path among all plug in boards.

e.g., VME bus, Multibus II, Futurebus+.

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VME (Versa Module Europe) bus: It was designed by Motorola to provide a high performance bus for 68000 based systems (IEEE P1014)

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Multibus: It was designed by Intel to provide a system bus for 8080 (IEEE 796).

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Buses

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ISA bus: (Industry Standard Architecture bus) 1984. This is a 16 bit bus standard which runs at 8.33 MHz. The vast majority of peripheral add –in cards like modems, sound cards, CD ROM interfaces and other low bandwidth applications are still ISA based. It is also called as Advanced Technology bus (AT bus)

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EISA bus: (Extended Industry Standard Architecture bus) 1988. This 32-bit bus standard runs at a speed of 8.33 MHz.

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Local bus: Buses implemented on printed circuit boards are called local buses.

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Buses

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MCA: (Micro channel Architecture) 1987. IBM introduced MCA along with the PS/2 computer. It handles 32 bits of data at a time, and it has a primitive intelligence to allow it to adjust to the system automatically.

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Buses

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PCI: (Peripheral Components Interconnect) 1992.

• It is a 64 bit standard, but is currently only implemented as 32 bits.
• It performs asynchronously to the main CPU, meaning that the PCI bus operates at 33 MHz regardless of the CPU clock.
• It also allows more than two devices on the bus, unlike VLB.
• Maximum bus length is 0.5 m.
• The maximum number of devices that can be connected to PCI bus is 1024 with multiple bus segments and at most 32 devices/bus segment.

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PCI

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AGP: (Accelerated Graphics Port) 1997. Intel introduced it as an improvement over the PCI bus. It is designed for a special type of video card.

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VESA Local Bus (VLB): Video Electronics Standards Association local bus is a 32-bit bus originally designed to provide higher bandwidth for video cards than is available with the ISA bus. It is optimized for the 486 CPU and can run at speeds up to 40 MHz with one card on the bus or up to 33 MHz with two cards on the bus. The speed of the VLB is dependent, and runs synchronously with the main system CPU.

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Buses

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SCSI: (Small Computer System Interface). An input and output bus that provides a standard interface between the processor and peripheral devices. Basic data bus width is 8-32 bits and maximum bus length is 25 meters.

• Introduced by Apple in 1984
• Used to interface a wide variety of high speed devices to the computer system.
• While called a bus it is really a mechanism to daisy chain devices together.

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SCSI Bus

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• SCSI-I
• Used 8 bit data bus width
• 5 MHz clock – transfer rate of 5 MB/sec
• Supported up to 7 devices (compare to the 2 of a typical IDE configuration)
• SCSI-2
• Current standard
• Expands the bus width to 16 or 32 bits
• Clock rate of 10 MHz
• Supports a wide variety of device types, making I/O software in the host simpler.

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SCSI Bus contd..

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• IDE: (Integrated Drive Electronics): It is a hard disk interface standard. In this, the hard disk controller circuit is located on the drive itself.
• EIDE: (Enhanced Integrated Drive Electronics)
• GPIB (General Purpose Interface Bus) (IEEE 488): It is a 24 pin parallel interface bus used to connect scientific instruments together or to a computer.

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IDE

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USB: (Universal Serial Bus) 1997. It is designed for low speed devices such as keyboards, mice, still cameras, snapshot scanners, digital telephones and so on. There are two kinds of USB ports: USB1, that supports up to 12 Mbps data speeds and USB2, that supports up to 480 Mbps data speeds. They have the following salient features:

• Users need not set switches or jumpers on boards or devices and open the case to install new I/O devices and reboot after installing a new device (plug and play)
• There will be only one kind of cable for connecting all devices.
• I/O devices will get their power from the cable.
• Up to 127 devices can be attached to a single computer.
• The system will support real time devices (e.g., sound, telephone)
• Devices can be installed when the computer is running.
• Transfer data much faster than the serial and parallel ports.

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USB

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Firewire (IEEE 1394): Designed to connect devices such as digital camcorders, digital cameras, digital video disc players, CD-ROM drives, printers, scanners and hard drives. It also enables high speed data communication, such as video conferencing and video editing, and gives data transfer speeds up to 1.6 Gbps.

• High speed, low cost serial link
• Gaining support in consumer electronics products as well as computer systems
• Deliberately move away from parallel connections with associated high cable and connector costs
• Provide high speed serial link (25-400 Mbps) that is able to connect to many devices
• Daisy chain up to 63 devices together on 1 bus, interconnect up to 1022 buses together through bridging techniques
• Communication is based on a 3 layer protocol
• Physical layer
• Link layer
• Transaction layer

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Firewire

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Recap

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Video Links

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• Peripheral Devices by Sudhakar Atchala
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